This invention relates to internal combustion engines, and more particularly to hydraulic valve lifters for small engines used on lawn mowers, snow blowers, generators and the like.
Valve lifters have been used for some time in automobile engines to open the intake and exhaust valves of the cylinder by lifting them off of their valve seats. A typical valve lifter is positioned in the valve train assembly between a cam located on a camshaft and the valve stem or push-rod that is interconnected with the valve itself. A cam follower, typically a face surface on the lifter, engages a cam on the camshaft to move the lifter in an upward direction, thereby also moving the valve stem or push-rod to open the valve.
One function of the valve lifter is to prevent unnecessary engine noise caused by air gaps in the valve train assembly. As the push-rod, valve stem, valve lifter, or other components in the valve train wear due to use, gaps appear between these components. To prevent unnecessary noise or engine clatter, the valve lifter is often manually-adjustable to remove these gaps. A typical manually-adjustable valve lifter uses a thread and nut arrangement, with the nut being turned by a wrench to extend the length of the valve lifter and remove the air gap.
More recently, hydraulic valve lifters have been used which are largely self-adjusting. In a hydraulic valve lifter, an outer cylinder has an axial bore in which a plunger or piston is located, as well as a hydraulic fluid and typically a spring mechanism. The axial movement of the outer cylinder in response to cam rotation causes the piston to axially move as well, with the compression of the spring mechanism and the hydraulic fluid preventing gaps in the valve train assembly. The valve train load is thus supported by the hydraulic fluid, the piston, and the spring.
Hydraulic valve lifters by definition require a hydraulic or working fluid to operate. In a typical prior art hydraulic valve lifter, the hydraulic fluid is supplied from the engine's pressurized lubrication system via an oil pump or the like. In such devices, the hydraulic fluid, which is typically oil or another lubricating fluid, is pumped by an oil pump through various piping into a reservoir or chamber in the hydraulic valve lifter. One disadvantage of such prior art hydraulic lifters is the additional costs of the oil pump and the required piping to provide a pressurized fluid to the lifter.
Another disadvantage of such prior art lifters is that they are not suitable for use on certain small engines that do not require an oil pump to lubricate the other moving components of the engine. If the engine uses a pressurized lubricating system to lubricate moving components such as the crankshaft and the piston connecting rods, then that oil pump may also be used to supply pressurized fluid to the hydraulic valve lifter. However, many single or two-cylinder engines do not use a pressurized lubricating system, and thus do not have an oil pump. Such engines typically use a so-called splash method of lubrication, in which a rotating shaft--typically in an oil slinger mechanism--passes through the crankcase oil and flings or splashes the oil onto other engine components to lubricate them. Engines using the splash system of lubrication typically have not used hydraulic valve lifters since such engines do not have oil pumps to provide pressurized fluid to the lifters, and since it is not economically feasible to provide a pressurized lubricating system merely for use with the hydraulic valve lifters. In short, small engines using the splash method of lubrication have typically been noisier during operation since heretofore the quieter hydraulic valve lifters have been unsuitable for use with such engines.